Somewhere back in the dim and distant I heard that "The Great Speckled Bird" came from a visual image of an open Bible. The open pages form wings on either side, and the letters make them look speckled. I can't vouch for any truth in that derivation, but I like it. And it seems more fitting for a country song than some scholarly glosses on the Book of Jeremiah. Certainly the Bible being identified with the church could have led to combining the images.